Sound-radiating system



Oct. 15, 1929. c, so 1,731,570

SOUND RADIATING SYSTEM Filed May 24, 1928 fl hrazfan 6/7/ arr/(50a Z my Patented Oct. 15, 1929 UNITED s'mrss PATENT arms HENRY c. HARRISON, OF roar WASHINGTON, NEW YORK, ASSIG'NOR 'ro WESTERN ELECTRIC COIQIIPANY, INCORPORATED F NEW. YORK, N. Y.,

EW Yo K Application filed May 24,

This invention relates to'sound radiating systems. i

An object of this invention is to reduce reflect-ion losses in a sound radiating system. Another object is to improve ,the' radiation of sound by'providing a,vibratory. member in which the transmission velocity is the same as the velocity of sound in air.

In general the sound radiating device of this invention comprises a mechanical transmission line having vibrations impressed on it at one point 'and arranged to dissipate energy all along its'length.v The line may be either of the smooth type or the type having lumped constants, the property of disslpa-tingenergy being analogous to the resistance of,an electric line. ;By proportioning the' eQnstantS of'the" line so that its impedance matches'the' -impedance of the actuating device and is substantially independent ofir'equency, so that the energy impressed on it issubstantially all dissipated before the vibrations reach the end, and so that the velocity of propagation along it is substantially equal to the velocity of sound in air; it is possible to construct an efficient high quality sound radiator.

In accordancewith one form of this invcntion, reflection losses in a sound radiating system are substantially eliminated by hav ing the system present a constant impedance to the impressed vibratory energy and by having the system sutliciently extensive that .practically all the energy is transferred to the air before the boundaries of the system are reached. It will be preferable in some cases to have the vibrating memberor system of such a character that the transmission velocity in the system is substantially the same as the velocity of sound in air. Such a system in one formof this invention comprises a long tube of paper or other flexible material of relatively small diameter compared to its length and having the surface corrugated or crimped. By having the vibratory energy to be radiated, impressed simultaneously upon all parts of the circumference at one end of the tube, the vibra 'tory energy in passing along the tube will A CORPORATION or SOUND-RADIATING sYsTEM 1923. Serial No. 641,059.

' stantially all of. the vibratory energy has been dissipated. The crimps or corrugations may be made deep enough to make theeffective transmission velocity-in the paper the same as the velocity of the associated sound in air thereby improving the quality and volume of sound radiation.

Referring to the drawings, Fig. 1 discloses this invention embodied in a long corrugated tube; Fig. 2 is an end viewof Fig. 1'; Fig.- 3 discloses a sound radiating member comprising a crimped sheet ;'Fig. 4 is a-sectional view of Fig. 3; Fig. 5 represents this invention embodied in a diaphragm ofparticular con struction; Fig. 6 is-a sectional View of F ig. 5 and Fig. 7 illustrates a sound'radiating system comprising a series'of diaphragms' or cones elastically coupled together.

Fig. 1 discloses atelephone receiver element 8 having its armature connected by a rod 9 to the end of a crimped, embossed, or corrugated tube 10. One possible arrangement for connecting the receiver armature to the tube 10 is by attaching a stiff plate 11 to the end of the tube and rigidly fastening rod 9 thereto. This insures that the vibratory energy impressed upon the tube from the receiver element will be simultaneously impressed upon all points of the circumference at one end of the tube. The vibratory energy so impressed passes along the corrugated tube until all of the energy has been dissipated or radiated into the air as sound waves.

If desired, the tube 10 may be made of such a length that during the normal operation of the device, substantially all of the vibratory energy will be dissipated before the end 12 of the tube is reached. This will insure that there will be no reflection losses from the boundaries of the radiating system, which would otherwise tend to distort the radiated energy by having the crimpe d tube 10 more responsive to vibrations of certain frequencies than others.

The crimps or corrugations in the tube should preferably be of such a size that the vibratory energy transmitted along the tube will at all times be in phase with the assos where s and mare the elasticity and mass per unit length. Without the corrugations the velocity would be several times that of sound in air, but by'corrugating the tube the elasticity may be decreascdcnough to reduce the velocity along the tube to the velocity of sound in air. tube is corrugated, the effective mass per unit length -also becomes: greater and this cfiect also aids in bringingzdown-the velocity value."

The construction described above enables the vibratory energy .to be impressed upon all parts of the circumference at :one end of the tube and if the tube is made of uniform material, it follows that-the :vibratoryenergy will encounter a constant mechanical impedance during its transmission along the tube; 1 This prevents reflection losses which results avhen'mechanicalvibratory energy is transmitted between mechanical devices having widely difi'enent- .impedances.

Thetube '10 is preferably made'of some flexible matenial. suohas paper. although various other material-ls may be employed depending u porn the radiation chamcteri'stic desired.

Another form that this invention may take is disel0Sed=-in Figs...3 and A: in'which the sound ,radiating system connected to the rma-tuve 1.8 of a receiver comprises a crimped sheet 160i paper or other flexible material.- The-vibratory energy 'from the armature of the receiver should prefierably be simultaneously-impressed upon all parts of the edged? of't-he papeijfand this may be insured-by having the rod '18 connected to a stilt member which extends along the edge 17 of the paper and fastened thereto. The same result may also-be-elfectively obtained by connecting the armature to a plurality of points along the-edge 17 of the paper as shownin the drawing by other connecting members 19 and 20. The sheet 16 may, as shown, he corrugated in the mme manner as the'crimped tuhe'of Fig. 1 in order to insure thatthe effective transmission of the vi bratory energy alongthe'sheet is substantially the same as the velocity of sound in air.

The sound radiating member disclosed in Figs. 1 and -3 may be supported in any desired manner, and may in general, be freely suspended from. the receiver armature, being connected to the armature at one end and angi g f e t the other e d. Other possible arrangements. for mounting these sound adiat ng members ill occu to those sk lled in the art,

Oi 6 1 88 as the- The forms of this invention disclosed in Figs. 1 and 3 illustrate how this invention may be applied to sound radiating systems which are subjected to longitudinal vibra lions. Fig. 5 illustrates one of the forms this invention may possess in which tlexural Vibrations of a sound radiating member are produccd by the receiver armature or other source of mechanical vibrations to be radiated. As disclosed more clearly in Fig. 6, the vibrating member is of a composite structure comprising two diaphragms 22 and .23 separated by a crinipcd diaphragm 24, the crimps or corrugations in which are circular. The armature of the associated receiver element is wnnccted by rod rto the ccnt-erof one of thediaphragms The two discs 22 and 23 may be made of any light flexible material such as paper, wood or aluminum. These discs are preferably given a tapered thickness, being considerably thicker at their center than at their edge so that the degree of tapering may-be adjusted to insure that the vibratory energy impressed upon the center of the disc will encounter a constant impedance in its transmission to the boundaries. The crimp sheet 24 may be made to increase the velocity of the vibratory energy to an extent.- sufiicient to make the velocity of the transmission of the vibratory energy from the center to the boundaries of the system substantially the same-as the velocity of sound in air. If desired, the sound radiating member of Fig. 6 may be freely suspended from the receiver armature.

It is contemplated that the .sound radiating members of Figs. 1, 3 or 5 will, in many cases, be made fairly extensive and such that the tubeot Fig. 1 may be three to ten feet long or longer and the discs of Fig. 6 may be several feet in diameter. This will insure an ctiicicnt radiation of the vibratory energy without the employment of large horns such as are now employed in some cases to couple small receiver diaphragms to a relatively large column of air.

In Fig. 7, the sound radiating system comprises a plurality of still cones coupled together in a suitable manner by an elastic means such as an elastic cord 31. The armature of the receiver element 32 is balanced by means oi a suitable spring 33 to hold the armature in position against the downwardpull exerted by the masses 30. A suitable support 3% is shown, between the arms of which are connected the elastic cord 31 and the spring member 33. The cones 30 are preterably of st-illenedmatcrial so aseto present to the vibratory energy a substantially pure mechanical resistance. It has been pointed out in my Patent No. 1,678,116, issued July 24, 1928, that a series of masses such as 30 coupled by elastic means may be made to have a substantially constant impedance for frequencies below a definite cut-off frequency defined by the following equation c m in which m is the mass per section and s is the shunt elasticity per section. The elastic string 31 may be made of any suitable mate'- rial having the desired elasticity and in general, it. may consist of rubber. The cones 30 may be made of metal or paper or any other material which can be stiffened so as to vibrate as a unit. Any desired number of cones 30 may be suspended from the armature and as many as fifteen or twenty may be employed and subjected to vibrations from the armature of a single receiver as long as the total mass does not become excessive. If the mass of each cone and the elasticity of the coupling means between adjacent cones are made to have values fulfilling the above equation, the vibrating system comprising the cones 30 and the elastic string 31 will present for all frequencies below the cut-off frequency a substantially constant impedance to mechanical vibrations impressed thereon, and a sufficient number ployed to insure that substantially all of the impressed vibratory energy is dissipated before the last cone remote from the receiver is reached. This means that the cone next to the receiver will vibrate with the greatest amplitude and the amplitude of vibrations of the remaining cones will decrease as one proceeds away from the receiver until when the other end of the system is reached, where the cone at the end will vibrate a negligible amount or may not vibrate at all.

In each of the figures of the drawing, a receiver element has been shown conventionally as the source of vibrations that are impressed upon the various sound radiating systems disclosed. It is obvious, of course, that this invention is not limited to a sound radiating member for a telephone receiver element, but may be readily applied to other systems besides electrical systems such as the phonograpl'i. in which means are employed for radiating sound waves corresponding to a sound record.

The armature disclosed for vibrating the members of Figs. 1, 3, 5, or 7 will have a certain mechanical impedance due to its mass and as disclosed in my copending application Serial No. 225.500, filed October 11, 1927. a shunt elasticity such as an elastic reed may be combined with the mass of the armature so that the mechanical impedance of the combination is substantially constant over a wide frequency range. It therefore follows that if the mechanical impedance of the sound radiating member matches the mechanical impedance of the armature no transition loss will take place as the vibratory enof cones may be emergy flows from thearmature into radiating member. It is to be understood that theforms of this invent-ion ,described'above are only typical and that the invention possesses widely different embodiments without departing in anywise. from .the spirit of this invention as defined in the appended claims. N

The invention claimed is:

I '1. A sound radiating system comprising a crimped-cylinder, and ineans attached to said cylinder for impressing .speech frequency mechanical vibrations thereonf 52A sound-radiatingrsystem comprising a cylinder; having a corrugated surface, the corrugations in. "saidsurface being at right ang'les to the'axis of-thecylinder.

A sound radiating member comprising a cylinder having 11av corrugated surface, and means attached to'one end of said cylinder for impressingh' speech; frequency; vibrations thereon.

tr-A lsound radiating member comprising a hollowibod y of light material having. a cor rugate'd surface," the elasticity and mass of said body'being suclras topresent a substantially constant cimpedance to speech vibrat-i'ons impressed thereon as the 1 vibrations pass from the point of application-to the boundaries the sound thereof- 5. A sound reproducer comprising a directacting-soundmadiator', and means for imparting lvibra'tory forces tliereto, said radiator having- 'siioli-"lelastieityi and mass per unit length as to produce a velocity of propagation of vibratory energy therein approaching the velocity of sound in air.

6. A sound reproducing device comprising a sound radiating surface and means for imparting vibrational forces thereto, said surface having its mass and elasticity coefiicients per unit length such as to produce a velocity of propagation of'vibratory energy substanti ally the same as the velocity of sound in air and of length such that substantially all of the vibratory energy imparted thereto will be dissipated by the time it reaches the boundary of the surface whereby reflection losses are substantially eliminated.

7. A sound radiating member comprising a material having inherently a rate of propagation of vibratory energy therein greater than the velocity of sound in air and having means for changing the elasticity of said material to an extent such that the velocity in said material is substantially the same as the velocity of sound in air.

8. A device for radiating sound directly into the air without the use of a horn comprising a member having successive sections thereof from the point of drive outwardly so proportioned with respect to their mass, elasticity and energy dissipation, that the member presents a substantially uniform impedance to vibratory forces :over a wide range of frequencies in the audible range.

9. A device forrradiating sound directly into the surrounding-air requiring no sound box or horn comprising a radiator unsupported at all parts except at'therpart where it is driven, having elasticity andmass coefficients per unit length and-of sufiicient length to offer a substantially constant impedance (to vibrations due=to speech frequencies impressed on a part of said device as the vibrations-pass from the point of application to the boundaries of the device. l

10. A direct-acting sound radiator having its mass and elasticity per unit length such as to present a substantially constant impedance to vibratory forces impressed thereon and of suflicient length to dissipate the energy of the vibratory forces into the airbefore the edge of the radiator, farthest removed-fromathe point of application of the vibratory forces, is reached.

11. A device :for radiating sounddirectly into the surrounding airy-requiring no sound box or horn, comprising a radiator adapted to be vibrated and having mass and elasticity per unit lengthsuch that-=the radiator will transmit with uniform efficiency vibrations of a broad band-of frequencies within the speech range, and means for impressing mechanical vibrations thereon.

In; witness whereof; I hereunto subscribe my name this 18th day of May A. D., 1923. HENRY C. HARRISON. 

